Congestive heart failure (CHF) is a significant health care problem which currently accounts for 7% of total health care expenditures in the USA. Approximately 400,000 new cases of heart failure are identified annually. The primary cause for development of heart failure is ischemic heart disease, and most new cases occur after myocardial infarction. The number of hospital discharges for heart failure has increased from 377,000 in 1979 to 875,000 in 1993, and the number of deaths during the same period has risen 82.5%. The average mortality rate 8 years following initial diagnosis is 85% for men and 65% for women.
The development of CHF begins as an injurious process to the myocardium that reduces cardiac function (especially contractile or pump function) either in a specific region(s) or throughout its entire extent (i.e., globally). Heart failure is said to exist whenever the myocardial injury is of sufficient severity to reduce the heart's capacity to pump an adequate output of blood to satisfy the body's tissue requirements either at rest or during exercise. The disease state of heart failure is not a static situation, but instead progressively worsens until death occurs either suddenly (e.g., by cardiac arrhythmia or embolism to the brain or lung) or gradually from pump failure per se. The progressive decline in heart function in patients with CHF is characterized by progressive enlargement of the ventricular chambers (i.e., ventricular dilatation) and thinning and fibrosis of the ventricular muscle. The progressive ventricular enlargement and accompanying histologic changes in the ventricular muscle are termed "remodeling", a process that involves changes in myocardiocyte structure as well as changes in the amount and composition of the surrounding interstitial connective tissue. An important constituent of the interstitial connective tissue is a matrix of fibrillar collagen, the "tissue scaffolding" that contributes to the maintenance of proper ventricular geometry and structural alignment of adjoining cardiomyocytes. The interstitial collagen matrix is subject to increased dissolution and repair during "remodeling" that leads to ventricular enlargement and progressive heart failure. The deterioration of the collagen matrix is effected by increased activity of matrix metalloproteases, the inhibition of which is a new treatment for heart failure and ventricular dilatation. Ventricular dilatation, the severity of which is measured by the end-diastolic and end-systolic volumes, is a prognostic marker of the probability of subsequent morbidity and mortality. The larger the ventricular chamber dimensions, the greater the likelihood of subsequent morbid events. Not only is pump function impaired by remodeling and ventricular dilation, but the enlarged chambers are prone to formation of clots, which can lead to stroke or embolism to other major organs (e.g., kidney, legs, intestinal tract).
Standard treatment for heart failure utilizes diuretics to decrease fluid retention, angiotensin converting enzyme inhibitors (ACE-Is) to reduce cardiac workload on the failing heart via vasodilation, and in the final stages of failure the positive inotrope digitalis to maintain cardiac output. Although ACE-Is have the benefit of increasing longevity unlike diuretics or positive inotropes, the beneficial effect of ACE-Is is limited to delaying death by only about 18 months. Clinical trials with .beta.-adrenergic blockers were recently conducted based on the hypothesis that reducing sympathetic drive would decrease the metabolic load on heart muscle cells. Unfortunately, this class of compounds was also found to not have a substantial effect on the progression of heart failure. The failure or limited success of previous heart failure therapies clearly shows that the controlling mechanism(s) mediating heart failure has not been targeted.
Drug development of the treatment of heart failure since the 1960s has focussed on cardiac muscle cells. The goal has been to reduce the workload on the cells, improve bloodflow to the cells, increase the contraction of the muscle, decrease the metabolic demand on cardiac myocytes, or some combination of these by various means. Focus on cardiac myocytes may have served to focus attention too far downstream. Overt heart failure may be caused by the breakdown of cardiac connective tissue. The breakdown in cardiac connective tissue proteins thus mediates cardiac dilation, one of the earliest characteristics of heart failure.
We have now discovered that compounds which inhibit the enzymes that mediate the breakdown of connective tissues are useful for treating heart failure and associated ventricular dilatation. Such enzymes are known as native matrix metalloproteinases, which are classes of naturally occurring enzymes found in most mammals. They are zinc proteases that hydrolyze collagens, proteoglycans, and glycoproteins. The classes include gelatinase A and B, stromelysin-1 and -2, fibroblast collagenase, neutrophil collagenase, matrilysin, metalloelastase, and interstitial collagenase. These enzymes are implicated with a number of diseases which result from breakdown of connective tissues, such as rheumatoid arthritis, osteoarthritis, osteoporosis, multiple sclerosis, and even tumor metastasis. To date, inhibitors of matrix metalloproteinases have not been utilized to treat heart failure or prevent ventricular dilatation. An object of this invention is to provide a method for treating and preventing heart failure and ventricular dilatation by administering a matrix metalloproteinase inhibitor.